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Drained agricultural peatlands occupy only 1% of agricultural land but are estimated to be responsible for approximately one third of global cropland greenhouse gas emissions. However, recent studies show that greenhouse gases fluxes from agricultural peatlands can vary by orders of magnitude over time. The relationship between these hot moments (individual fluxes with disproportionate impact on annual budgets) of greenhouse gas emissions and individual chamber locations (i.e. hot spots with disproportionate observations of hot moments) is poorly understood, but may help elucidate patterns and drivers of high greenhouse gas emissions from agricultural peatland soils. We used continuous chamber-based flux measurements across three land uses (corn, alfalfa, and pasture) to quantify the spatiotemporal patterns of soil greenhouse gas emissions from temperate agricultural peatlands in the Sacramento-San Joaquin Delta of California. We found that the location of hot spots of emissions varied over time and were not consistent across annual timescales. Hot moments of nitrous oxide (N2O) and carbon dioxide (CO2) fluxes were more evenly distributed across space than methane (CH4). In the corn system, hot moments of CH4 flux were often isolated to a single location but locations were not consistent across years. Spatiotemporal variability in soil moisture, soil oxygen, and temperature helped explain patterns in N2O fluxes in the annual corn agroecosystem but were less informative for perennial alfalfa N2O fluxes or CH4 fluxes across ecosystems, potentially due to insufficient spatiotemporal resolution of the associated drivers. Overall, our results do not support the concept of persistent hot spots of soil CO2, CH4, and N2O emissions in these drained agricultural peatlands. Hot moments of high flux events generally varied in space and time and thus required high sample densities. Our results highlight the importance of constraining hot moments and their controls to better quantify ecosystem greenhouse gas budgets. [ABSTRACT FROM AUTHOR]

Agricultural peatlands are estimated to emit approximately one third of global greenhouse gas (GHG) emissions from croplands, but the temporal dynamics and controls of these emissions are poorly understood, particularly for nitrous oxide (N2 O). We used cavity ring-down spectroscopy and automated chambers in a drained agricultural peatland to measure over 70,000 individual N2 O, methane (CH4 ), and carbon dioxide (CO2 ) fluxes over 3 years. Our results showed that N2 O fluxes were high, contributing 26% (annual range: 16%-35%) of annual CO2 e emissions. Total N2 O fluxes averaged 26 ± 0.5 kg N2 O-N ha-1 y-1 and exhibited significant inter- and intra-annual variability with a maximum annual flux of 42 ± 1.8 kg N2 O-N ha-1 y-1 . Hot moments of N2 O and CH4 emissions represented 1.1 ± 0.2 and 1.3 ± 0.2% of measurements, respectively, but contributed to 45 ± 1% of mean annual N2 O fluxes and to 140 ± 9% of mean annual CH4  fluxes. Soil moisture, soil temperature, and bulk soil oxygen (O2 ) concentrations were strongly correlated with soil N2 O and CH4 emissions; soil nitrate ( NO3- ) concentrations were also significantly correlated with soil N2 O emissions. These results suggest that IPCC benchmarks underestimate N2 O emissions from these high emitting agricultural peatlands by up to 70%. Scaling to regional agricultural peatlands with similar management suggests these ecosystems could emit up to 1.86 Tg CO2 e y-1 (range: 1.58-2.21 Tg CO2 e y-1 ). Data suggest that these agricultural peatlands are large sources of GHGs, and that short-term hot moments of N2 O and CH4 are a significant fraction of total greenhouse budgets.

Classrooms are fundamental components of university campuses. The creation of inclusive and equitable campus environments is incumbent upon the teachers who need to navigate through "hot moments", which typically refers to situations or incidents that generate intense emotions or strong reactions among the students or between the students and teachers. The literature suggests that many "hot moments" occur due to microaggressions in the classroom and that issues of difference, power, and privilege underlie "hot moments". Based on qualitative research done with university teachers in a Dutch institution, our research shows that teacher-described "hot moments" can be analyzed under three interrelated dimensions: individual, interactional, and institutional. We suggest educators and higher education policy makers read through these experiences as a way to better understand the challenges their colleagues face, most often alone as the classroom's leader; in the hope of advancing change efforts to create more inclusive and equitable class environments which will change how minoritized students experience university education. [ABSTRACT FROM AUTHOR]

Classrooms are fundamental components of university campuses. The creation of inclusive and equitable campus environments is incumbent upon the teachers who need to navigate through “hot moments”, which typically refers to situations or incidents that generate intense emotions or strong reactions among the students or between the students and teachers. The literature suggests that many “hot moments” occur due to microaggressions in the classroom and that issues of difference, power, and privilege underlie “hot moments”. Based on qualitative research done with university teachers in a Dutch institution, our research shows that teacher-described “hot moments” can be analyzed under three interrelated dimensions: individual, interactional, and institutional. We suggest educators and higher education policy makers read through these experiences as a way to better understand the challenges their colleagues face, most often alone as the classroom’s leader; in the hope of advancing change efforts to create more inclusive and equitable class environments which will change how minoritized students experience university education.

Nitrous oxide (N2O) is the contributor to agricultural greenhouse gas emissions with the highest warming global potential. It is widely recognised that traffic and animal-induced compaction can lead to an increased potential for N2O emissions by decreasing soil oxygen supply. The extent to which the spatial and temporal variability of N2O emissions can be explained by soil compaction is unclear. This review aims to comprehensively discuss soil compaction effects on N2O emissions, and to understand how compaction may promote N2O emission hotspots and hot moments. An impact factor of N2O emissions due to compaction was calculated for each selected study; compaction effects were evaluated separately for croplands, grasslands and forest lands. Topsoil compaction was found to increase N2O emissions by 1.3 to 42 times across sites and land uses. Large impact factors were especially reported for cropland and grassland soils when topsoil compaction—induced by field traffic and/or grazing—is combined with nitrogen input from fertiliser or urine. Little is known about the contribution of subsoil compaction to N2O emissions. Water-filled pore space is the most common water metric used to explain N2O emission variability, but gas diffusivity is a parameter with higher prediction potential. Microbial community composition may be less critical than the soil environment for N2O emissions, and there is a need for comprehensive studies on association between environmental drivers and soil compaction. Lack of knowledge about the interacting factors causing N2O accumulation in compacted soils, at different degrees of compactness and across different spatial scales, limits the identification of high-risk areas and development of efficient mitigation strategies. Soil compaction mitigation strategies that aim to loosen the soil and recover pore system functionality, in combination with other agricultural management practices to regulate N2O emission, should be evaluated for their effectiveness across different agro-climatic conditions and scales. [ABSTRACT FROM AUTHOR]

We evaluated the diversity and ecological network structure of insects associated with Cylindropuntia imbricata, a common cactus distributed throughout the Mexican high plateau (southern Chihuahuan desert). We performed a field assay where we randomly selected adult individuals of C. imbricata to analyze the effect of induced water stress on cacti. Our data revealed that insect diversity was higher as soil moisture increased; however, time of day highly influenced species composition. The results exhibited that ecological networks do not support stable interactions when cacti were watered. Probably, watering destabilized the nested pattern of the networks because is in attractive but short-lived resource for insects (hot moments). Time-subnetworks showed that watered cacti were nested only during the first hours of the day. Presumably, insect species responded to "hot moments" determined by induced soil moisture. The highest insect species composition and species interactions occurred at noon, demonstrating a threshold to avoid overheating and therefore, a temporal segregation of species during the day. Further research is needed to improve knowledge on environmental determinants such as water, as a critical issue to predict the impacts of climate change on species diversity and their trophic interactions, particularly in deserts where rains are scarce. [ABSTRACT FROM AUTHOR]

Nutrient-rich northern peatlands are often drained to enhance forest productivity, turning peatland soils into sinks of methane (CH _4 ) and sources of nitrous oxide (N _2 O). However, further attention is needed on CH _4 and N _2 O dynamics during the winter period to fully understand the spatio-temporal variability of fluxes. Besides soil, tree stems can also emit CH _4 and N _2 O. However, stem contribution is not considered in most biogeochemical models. We determined the temporal dynamics of winter-time CH _4 and N _2 O fluxes in a drained peatland forest by simultaneously measuring stem and soil fluxes and exploring the relationships between gas fluxes and soil environmental parameters. During sampling (October 2020–May 2021), gas samples from Downy Birch ( Betula pubescens ) and Norway Spruce ( Picea abies ) trees were collected from different tree heights using manual static chambers and analysed using gas chromatography. Soil CH _4 and N _2 O concentrations were measured using an automated dynamic soil chamber system. Tree stems were a net source of CH _4 and N _2 O during the winter period. The origin of stem CH _4 emissions was unclear, as stem and soil CH _4 fluxes had opposite flux directions, and the irregular vertical stem flux profile did not indicate a connection between stem and soil fluxes. Stem N _2 O emissions may have originated from the soil, as emissions decreased with increasing stem height and were driven by soil N _2 O emissions and environmental parameters. Soil was a net sink for CH _4 , largely determined by changes in soil temperature. Soil N _2 O dynamics were characterised by hot moments—short periods of high emissions related to changes in soil water content. Tree stem emissions offset the soil CH _4 sink by 14% and added 2% to forest floor N _2 O emissions. Therefore, CH _4 and N _2 O budgets that do not incorporate stem emissions can overestimate the sink strength or underestimate the total emissions of the ecosystem.

Abstract Nitrous oxide (N2O) is a potent greenhouse gas and major component of the net global warming potential of bioenergy feedstock cropping systems. Numerous environmental factors influence soil N2O production, making direct correlation difficult to any one factor of N2O fluxes under field conditions. We instead employed quantile regression to evaluate whether soil temperature, water‐filled pore space (WFPS), and concentrations of soil nitrate (NO3−) and ammonium (NH4+) determined upper bounds for soil N2O flux magnitudes. We collected data over 6 years from a range of bioenergy feedstock cropping systems including no‐till grain crops, perennial warm‐season grasses, hybrid poplar, and polycultures of tallgrass prairie species each with and without nitrogen (N) addition grown at two sites. The upper bounds for soil N2O fluxes had a significant and positive correlation with all four environmental factors, although relatively large fluxes were still possible at minimal values for nearly all factors. The correlation with NH4+ was generally weaker, suggesting it is less important than NO3− in driving large fluxes. Quantile regression slopes were generally lower for unfertilized perennials than for other systems, but this may have resulted from a perpetual state of nitrogen limitation, which prevented other factors from being clear constraints. This framework suggests efforts to reduce concentrations of NO3− in the soil may be effective at reducing high‐intensity periods—”hot moments”—of N2O production.

In arid and semi‐arid regions, many rivers experience extremely low flow conditions during seasonal dry periods. During these times, effluent from wastewater treatment plants can make up the majority of flow in the river. However, water quality in urban systems can also be strongly influenced by the natural or human‐influenced flow regime and discharge from other anthropogenic sources such as industrial operations and runoff from impervious surfaces. In this study, we aimed to determine whether water quality was controlled primarily by wastewater discharge in an effluent‐dominated river. Between May 2016–May 2019, we systematically measured water temperature, pH, dissolved oxygen, biochemical oxygen demand, and the concentrations of nitrate‐N, ammonia‐N, and orthophosphate in the South Platte River in the Denver metropolitan area, Colorado, USA. We found that, despite being an effluent‐dominated river, wastewater treatment plant discharge was not the principal factor controlling water quality in many of the sampled areas. Non‐point source pollution from impervious surfaces, delivered to the river through storm drains and minor tributary streams, also contributed to the high nutrient conditions in several locations. We also noted a strong seasonality in water quality, with higher concentrations of nutrients and higher biochemical oxygen demand in the winter months when wastewater effluent can make up more than 90% of the flow in the river. Thus, the interaction of discharge location and reduced seasonal flow produced spatio‐temporal hot spots of diminished water quality. More stringent enforcement of water quality regulations may improve water quality in this system. However, a large portion of the pollution seems to be from non‐point sources, which are very difficult to control. [ABSTRACT FROM AUTHOR]

Fecal bacteria in surface water may indicate threats to human health. Our hypothesis is that village settlements in tropical rural areas are major hotspots of fecal contamination because of the number of domestic animals usually roaming in the alleys and the lack of fecal matter treatment before entering the river network. By jointly monitoring the dynamics of Escherichia coli and of seven stanol compounds during four flood events (July-August 2016) at the outlet of a ditch draining sewage and surface runoff out of a village of Northern Lao PDR, our objectives were (1) to assess the range of E. coli concentration in the surface runoff washing off from a village settlement and (2) to identify the major contributory sources of fecal contamination using stanol compounds during flood events. E. coli pulses ranged from 4.7 × 10 4 to 3.2 × 10 6 most probable number (MPN) 100 mL -1 , with particle-attached E. coli ranging from 83 to 100%. Major contributory feces sources were chickens and humans (about 66 and 29%, respectively), with the highest percentage switching from the human pole to the chicken pole during flood events. Concentrations indicate a severe fecal contamination of surface water during flood events and suggest that villages may be considered as major hotspots of fecal contamination pulses into the river network and thus as point sources in hydrological models.

Algal blooms in the Great Lakes are a concern due to excess nutrient loading from non-point sources; however, there is uncertainty over the relative contributions of various non-point sources under different types of land use in rural watersheds, particularly over annual time scales. Four nested subwatersheds in Southern Ontario, Canada (one natural woodlot, two agricultural and one mixed agricultural and urban) were monitored over one year to identify peak periods ('hot moments') and areas ('hot spots') of nutrient (dissolved reactive phosphorus, DRP; total phosphorus, TP; and nitrate, NO 3 −) export and discharge. Annual nutrient export was small at the natural site (0.001 kg DRP ha−1; 0.004 kg TP ha−1; 0.04 kg NO 3 —N ha−1) compared to the agricultural and mixed-use sites (0.10–0.15 kg DRP ha−1; 0.70–0.94 kg TP ha−1; 9.15–11.55 kg NO 3 —N ha−1). Temporal patterns in P concentrations were similar throughout the sites, where spring was the dominant season for P export, irrespective of land use. Within the Hopewell Creek watershed, P and N hot spots existed that were consistently hot spots across all events with the location of these hot spots driven by local land use patterns, where there was elevated P export from a dairy-dominated sub-watershed and elevated N export from both of the two agricultural sub-watersheds. These estimates of seasonal- and event-based nutrient loads and discharge across nested sub-watersheds contribute to the growing body of evidence demonstrating the importance of identifying critical areas and periods in which to emphasize management efforts. [ABSTRACT FROM AUTHOR]

As the primary microbial substrate after shoot cutting, the element stoichiometry of root-detritus (dying or dead roots) influences the enzyme activity in root-detritusphere. However, the effect of the C/P ratio of root-detritus on the dynamics and distribution of enzyme activities is little revealed. We hypothesised that P fertilisation would decrease the C/P ratio of root-detritus, therefore affecting the hotspot areas and hot moments of C-acquiring and P-acquiring enzyme activities, as well as their activity ratio (C/P acquisition ratio). Root-detritus of low (59.0) and high (170.8) C/P ratios was produced in P-poor soil with and without P fertilisation, respectively. In situ soil zymography showed that the distribution of C-acquiring enzymes (β-glucosidase and cellobiohydrolase) was more associated with root-detritus than P-acquiring enzymes (acid and alkaline phosphomonoesterase). P fertilisation increased the hotspot areas of C-acquiring enzyme activities over the experiment, without influencing their temporal dynamics. However, its effect on phosphomonoesterase activities depended on the decomposition and delayed the appearance of the highest hotspot areas. P supply met the microbial demand in P-fertilised soil, with high C/P acquisition ratio and constant stoichiometry of microbial biomass C (MBC)/microbial biomass P (MBP). A low C/P acquisition ratio and high MBC/MBP in non-fertilised soil was observed, indicating P limitation for microorganisms. After the 150-day incubation, Olsen P significantly increased in P-fertilised soil (P < 0.05), whereas it decreased in the root-detritusphere of non-fertilised soil. We conclude that the decomposition of root-detritus with a low C/P ratio has potential to improve soil P availability; however, C-P imbalance may increase during the decomposition of root-detritus with a high C/P ratio. [ABSTRACT FROM AUTHOR]

Nitrous oxide (N2O) is a potent greenhouse gas and major component of the net global warming potential of bioenergy feedstock cropping systems. Numerous environmental factors influence soil N2O production, making direct correlation difficult to any one factor of N2O fluxes under field conditions. We instead employed quantile regression to evaluate whether soil temperature, water‐filled pore space (WFPS), and concentrations of soil nitrate (NO3−) and ammonium (NH4+) determined upper bounds for soil N2O flux magnitudes. We collected data over 6 years from a range of bioenergy feedstock cropping systems including no‐till grain crops, perennial warm‐season grasses, hybrid poplar, and polycultures of tallgrass prairie species each with and without nitrogen (N) addition grown at two sites. The upper bounds for soil N2O fluxes had a significant and positive correlation with all four environmental factors, although relatively large fluxes were still possible at minimal values for nearly all factors. The correlation with NH4+ was generally weaker, suggesting it is less important than NO3− in driving large fluxes. Quantile regression slopes were generally lower for unfertilized perennials than for other systems, but this may have resulted from a perpetual state of nitrogen limitation, which prevented other factors from being clear constraints. This framework suggests efforts to reduce concentrations of NO3− in the soil may be effective at reducing high‐intensity periods—"hot moments"—of N2O production. Quantile regression between soil N2O fluxes and environmental parameters. Lines indicate the quantile regression relationship between parameters at τ = 0.95, approximately reflecting the relationship that determines the 95th percentile of fluxes. Regressions were calculated independently for each environmental parameter. Flux data and soil inorganic N concentration data were inverse hyperbolic sine (IHS) transformed for regression and are presented on a transformed scale. Individual observations are partially transparent to illustrate observation density. All slope and intercept terms were significant at p < 0.05. [ABSTRACT FROM AUTHOR]

Nutrient and sediment transport exhibit strong spatial and temporal inequality, with a small percentage of locations and events contributing to the vast majority of total annual loads. The processes for determining how to reduce total annual loads at a watershed scale often target spatial, but not temporal, components of inequality. We introduce a framework using Lorenz Inequality and corresponding Gini Coefficient to quantify the temporal inequality of nutrient and sediment transport across the Chesapeake Bay watershed. This long-impaired, 166 000 km ^2 watershed has been federally mandated since 2010 to continually reduce nutrient and sediment loads reaching the Bay. Data were obtained for 108 sites in the Chesapeake Bay’s non-tidal network from 2010 to 2018. The Lorenz Inequality and Gini Coefficient analyses were conducted using daily-scale data for flow and loads of total nitrogen (TN), total phosphorus (TP), and total suspended sediment (TSS) at each gaging station. We leverage these results to create a ‘temporal targeting framework’ that identifies periods of time and corresponding flow conditions that must be targeted to achieve desired or mandated load reduction goals across the watershed. Among the 108 sites, the degree of temporal inequality for TP and TSS (0.37–0.98) was much greater than for flow and TN (0.29–0.77), likely due to the importance of overland versus baseflow in the transport pathways of the respective constituents. These findings stress the importance of informed design and implementation of best management practices effective in ‘hot moments,’ and not just ‘hot spots,’ across impaired watersheds to achieve and maintain water quality restoration goals. The ‘temporal targeting framework’ detailed in this manuscript provides a useful and convenient method for watershed planners to create low- and high-flow load targeting tables specific to a watershed and constituent.

Efforts have been made in recent years to improve knowledge about soil greenhouse gas (GHG) fluxes from sub-Saharan Africa. However, data on soil GHG emissions from smallholder coffee-dairy systems have not hitherto been measured experimentally. This study aimed to quantify soil GHG emissions at different spatial and temporal scales in smallholder coffee-dairy farms in Murang'a County, Central Kenya. GHG measurements were carried out for one year, comprising two cropping seasons, using vented static chambers and gas chromatography. Sixty rectangular frames were installed on two farms comprising the three main cropping systems found in the area: 1) coffee ( Coffea arabica L.); 2) Napier grass ( Pennisetum purpureum ); and 3) maize intercropped with beans ( Zea mays and Phaseolus vulgaris ). Within these fields, chambers were allocated on fertilised and unfertilised locations to capture spatial variability. Cumulative annual fluxes in coffee plots ranged from 1 to 1.9 kg N 2 O-N ha − 1 , 6.5 to 7.6 Mg CO 2 -C ha − 1 and − 3.4 to − 2.2 kg CH 4 -C ha − 1 , with 66% to 94% of annual GHG fluxes occurring during rainy seasons. Across the farm plots, coffee received most of the N inputs and had 56% to 89% higher emissions of N 2 O than Napier grass, maize and beans. Within farm plots, two to six times higher emissions were found in fertilised hotspots – around the perimeter of coffee trees or within planted maize rows – than in unfertilised locations between trees, rows and planting holes. Background and induced soil N 2 O emissions from fertiliser and manure applications in the three cropping systems were lower than hypothesized from previous studies and empirical models. This study supplements methods and underlying data for the quantification of GHG emissions at multiple spatial and temporal scales in tropical, smallholder farming systems. Advances towards overcoming the dearth of data will facilitate the understanding of synergies and tradeoffs of climate-smart approaches for low emissions development. [ABSTRACT FROM AUTHOR]

Abstract: Indirect nitrous oxide (N2O) emissions from drainage ditches and headwater streams are poorly constrained. Few studies have monitored stream N2O emissions and fewer modeling studies have been conducted to simulate stream N2O emissions. In this study, we developed direct and indirect N2O emission modules and a corresponding calibration module for use in the Soil and Water Assessment Tool (SWAT) model, and implemented the expanded SWAT model (termed SWAT‐N2O) to a representative fourth‐stream‐order catchment (210 km2) and six first‐order stream catchments (0.22–1.83 km2) in southeastern Minnesota. We simulated the spatial and temporal fluctuations of the indirect emissions from streams, identified emission “hot spots” and “hot moments,” and diagnosed the correlations between direct and indirect emissions. We showed that zero‐order streams and first‐order streams could contribute 0.034–0.066 and 0.011 nmol N2O m−2 s−1 (expressed on the basis of unit catchment area) to the total surface emissions, respectively. Emissions from zero‐order and first‐order streams equal 24–41% of direct emissions from soil, which may explain the emission gap between calculations using top‐down and bottom‐up methods. Clear spatial patterns were identified for both direct and indirect emissions and their spatial variations were negatively correlated. Our results suggest that the IPCC N2O emission factor for streams in the Corn Belt should be increased by 3.2–5.7 times. Increasing precipitation and streamflow in the Corn Belt may potentially increase frequencies of soil anoxic conditions and nitrate leaching to streams, and subsequently increase N2O emissions from both soils and streams. [ABSTRACT FROM AUTHOR]

Abstract: Identifying hot spots and hot moments of nitrous oxide (N2O) emissions in the landscape is critical for monitoring and mitigating the emission of this potent greenhouse gas. We propose a novel use of the Lorenz curve and Gini coefficient (G) to improve the estimation of the mean as well as the spatial and temporal variation of N2O emissions from a bioenergy landscape. The analyses indicate that the G was better correlated (R2 = 0.72, P < 0.001) with daily N2O emissions than the coefficient of variation and skewness. A hot moment for N2O emissions occurred after a storm event, with a heterogeneous spatial distribution of N2O emissions (G = 0.65); in contrast, CO2 emissions remained spatially uniform throughout the same period (G = 0.36). Volumetric soil air content below 0.03 m3 m−3 occurred more frequently in the wetter footslope positions and created N2O hot spots, with a high temporal inequality during the growing season (G = 0.75). In contrast, well‐drained shoulder positions were cold spots, with uniformly distributed and low N2O emissions (G = 0.44). The spatial N2O inequality mirrored the landscape wetness generated by rain events, while biogeochemical equality prevailed in the landscape. The Lorenz curve and G are tools to standardize the spatial and temporal variation of N2O emissions across diverse landscapes and management scenarios. These two inequality indicators, in association with spatial maps, can help delineate the critical spatial mosaics and temporal windows of N2O emissions and guide landscape‐scale monitoring and mitigation strategies to reduce N2O emissions. [ABSTRACT FROM AUTHOR]

A restored riparian zone was characterized to understand the effects of flooding on subsurface hydrological flow paths and nitrate removal in groundwater. Field and laboratory investigations were combined with numerical modeling of dynamic flow and reactive nitrate transport. Flooding enhances nitrate removal in groundwater primarily by two mechanisms. First, by creating a stagnant flow zone beneath the flooded area thereby increasing the residence time and leaving more time for nitrate removal. Secondly, nitrate removal is increased by enhancing upward flow into the highly reactive organic-rich top layers. Flooding therefore contributes to nitrate removal in 'hot spots', where nitrate is transported to the peat and during 'hot moments', when flow is stagnant. The permeability of the capping peat layer relative to the aquifer is important as it controls both mechanisms. The model shows that the deep-seated nitrate removal is greater than projected from the laboratory nitrate reduction experiments. [ABSTRACT FROM AUTHOR]

Protecting or restoring aquatic ecosystems in the face of growing anthropogenic pressures requires an understanding of hydrological and biogeochemical functioning across multiple spatial and temporal scales. Recent technological and methodological advances have vastly increased the number and diversity of hydrological, biogeochemical, and ecological tracers available, providing potentially powerful tools to improve understanding of fundamental problems in ecohydrology, notably: 1. Identifying spatially explicit flowpaths, 2. Quantifying water residence time, and 3. Quantifying and localizing biogeochemical transformation. In this review, we synthesize the history of hydrological and biogeochemical theory, summarize modern tracer methods, and discuss how improved understanding of flowpath, residence time, and biogeochemical transformation can help ecohydrology move beyond description of site-specific heterogeneity. We focus on using multiple tracers with contrasting characteristics (crossing proxies) to infer ecosystem functioning across multiple scales. Specifically, we present how crossed proxies could test recent ecohydrological theory, combining the concepts of hotspots and hot moments with the Damköhler number in what we call the HotDam framework. [ABSTRACT FROM AUTHOR]

Terrestrial inputs into freshwater ecosystems are a classical field of environmental science. Resource fluxes (subsidy) from aquatic to terrestrial systems have been less studied, although they are of high ecological relevance particularly for the receiving ecosystem. These fluxes may, however, be impacted by anthropogenically driven alterations modifying structure and functioning of aquatic ecosystems. In this context, we reviewed the peer-reviewed literature for studies addressing the subsidy of terrestrial by aquatic ecosystems with special emphasis on the role that anthropogenic alterations play in this water–land coupling. Our analysis revealed a continuously increasing interest in the coupling of aquatic to terrestrial ecosystems between 1990 and 2014 (total: 661 studies), while the research domains focusing on abiotic (502 studies) and biotic (159 studies) processes are strongly separated. Approximately 35% (abiotic) and 25% (biotic) of the studies focused on the propagation of anthropogenic alterations from the aquatic to the terrestrial system. Among these studies, hydromorphological and hydrological alterations were predominantly assessed, whereas water pollution and invasive species were less frequently investigated. Less than 5% of these studies considered indirect effects in the terrestrial system e.g. via food web responses, as a result of anthropogenic alterations in aquatic ecosystems. Nonetheless, these very few publications indicate far-reaching consequences in the receiving terrestrial ecosystem. For example, bottom-up mediated responses via soil quality can cascade over plant communities up to the level of herbivorous arthropods, while top-down mediated responses via predatory spiders can cascade down to herbivorous arthropods and even plants. Overall, the current state of knowledge calls for an integrated assessment on how these interactions within terrestrial ecosystems are affected by propagation of aquatic ecosystem alterations. To fill these gaps, we propose a scientific framework, which considers abiotic and biotic aspects based on an interdisciplinary approach. [ABSTRACT FROM AUTHOR]

Conservation fences have been used as a tool to stop threatening processes from acting against endangered wildlife, yet little is known of the impacts of fences on non-target native species. In this study, we intensively monitored a pest-exclusion fence for 16 months to assess impacts on a reptile community in south-eastern Australia. We registered 1052 reptile records of six species along the fence. Encounters and mortality were greatest for eastern long-necked turtles ( Chelodina longicollis ), whereas impacts on lizards ( Tiliqua rugosa , Tiliqua scincoides , Pogona barbata , Egernia cunninghami ) and snakes ( Pseudonaja textilis ) were more moderate. We recorded several Chelodina longicollis recaptures at the fence and many of these were later found dead at the fence, indicating persistent attempts to navigate past the fence. We conservatively estimate that the fence resulted in the death of 3.3% and disrupted movements of 20.9% of the turtle population within the enclosure. Movement disruption and high mortality were also observed for turtles attempting to enter the nature reserve, effectively isolating the reserve population from others in the wider landscape. Of 98 turtle mortalities, the most common cause of death was overheating, followed by predation, vehicular collision, and entanglement. Turtle interactions were clustered in areas with more wetlands and less urban development, and temporally correlated with high rainfall and solar radiation, and low temperature. Thus, managers could focus at times and locations to mitigate impacts on turtles. We believe the impact of fences on non-target species is a widespread and unrecognized threat, and suggest that future and on-going conservation fencing projects consider risks to non-target native species, and where possible, apply mitigation strategies that maintain natural movement corridors and minimize mortality risk. [ABSTRACT FROM AUTHOR]

Vidon, Philippe, Craig Allan, Douglas Burns, Tim P. Duval, Noel Gurwick, Shreeram Inamdar, Richard Lowrance, Judy Okay, Durelle Scott, and Steve Sebestyen, 2010. Hot Spots and Hot Moments in Riparian Zones: Potential for Improved Water Quality Management. Journal of the American Water Resources Association (JAWRA) 46(2):278-298. DOI: 10.1111/j.1752-1688.2010.00420.x Biogeochemical and hydrological processes in riparian zones regulate contaminant movement to receiving waters and often mitigate the impact of upland sources of contaminants on water quality. These heterogeneous processes have recently been conceptualized as “hot spots and moments” of retention, degradation, or production. Nevertheless, studies investigating the importance of hot phenomena (spots and moments) in riparian zones have thus far largely focused on nitrogen (N) despite compelling evidence that a variety of elements, chemicals, and particulate contaminant cycles are subject to the influence of both biogeochemical and transport hot spots and moments. In addition to N, this review summarizes current knowledge for phosphorus, organic matter, pesticides, and mercury across riparian zones, identifies variables controlling the occurrence and magnitude of hot phenomena in riparian zones for these contaminants, and discusses the implications for riparian zone management of recognizing the importance of hot phenomena in annual solute budgets at the watershed scale. Examples are presented to show that biogeochemical process-driven hot spots and moments occur along the stream/riparian zone/upland interface for a wide variety of constituents. A basic understanding of the possible co-occurrence of hot spots and moments for a variety of contaminants in riparian systems will increase our understanding of the influence of riparian zones on water quality and guide management strategies to enhance nutrient or pollutant removal at the landscape scale. [ABSTRACT FROM AUTHOR]

Water is a crucial factor controlling the fate and processing of soil organics. Water commonly flows through the vadose zone via preferential flow pathways, resulting in nonuniform and rapid infiltration. Hence, a large portion of the soil matrix is bypassed. Preferential flow paths, often associated with well-connected macropore networks (>300 μm Ø), offer a unique balance between water availability, nutrient delivery, and re-oxygenation upon drainage. The heightened concentrations of moisture, nutrients, and oxygen make these locations optimal for high rates of microbial activity. Flow paths often display temporal stability. This stability results in repeated wetting and biogeochemical reactivation through time creating a lasting impact on micro-environmental conditions relevant to microbial functioning and carbon cycling in soil. Despite decades of research on preferential flow, there is still a need to link flow paths and the resultant heterogeneous moisture distributions to soil function. In this review, we discuss how preferential flow can serve as a framework of reference for the spatially and temporally heterogeneous biogeochemical cycling of soil carbon. We highlight the importance of combining current knowledge of pore-scale carbon dynamics with an appreciation of connected networks of hydraulically active pores/paths within the soil profile. Such combination opens new possibilities for upscaling pore-scale processes with the inclusion of resource heterogeneity at the macroscale. Working within this hydraulically connected framework can provide insight for the mechanistic representation of hot moments, which are temporally isolated large pulses of CO 2 after rewetting or thawing events. We conclude with suggestions on knowledge gaps and stress the critical need of linking soil physics with biology to mechanistically understand soil functions. • Preferential flow paths play a key role in soil carbon dynamics. • Pore-scale carbon dynamics could be upscaled using hydraulic connectivity. • A conceptual model is presented that considers how soil pores function from hydrological and microbial perspective. [ABSTRACT FROM AUTHOR]

To devise effective measures for reducing hazardous wildlife-vehicle collisions, it is necessary to know when during the year accidents occur most frequently, and what factors cause the seasonal patterns. Daylight Saving Time (DST) 1-h clock-shifts around the spring and fall equinoxes at temperate zone latitudes are associated with increased vehicle accidents, attributed to driver error caused by disrupted sleep patterns and changes in visibility during peak driving times. Collision with deer is a significant cause of motor vehicle accidents in North America; in New York State alone, 65,000 vehicle accidents annually are caused by collision with white-tailed deer (Odocoileus virginianus). We asked whether white-tailed deer-vehicle collisions (DVC) increased in frequency after DST clock shifts in New York State, by analyzing 35,167 New York State DVC reports from 2005 to 2007. For the spring, when the clock is shifted an hour forward relative to sunrise (i.e. later sunrise and sunset), there was either no change or possibly a small decrease in workweek evening DVC after the clock shift. For fall, when the clock is shifted an hour back relative to sunrise (i.e. earlier sunrise and sunset), the DVC rate was far higher than spring. The DVC rate was higher after the clock shift than before, caused in part by an ongoing seasonal trend for increasing DVC associated with deer behavior around the time of rut, peaking about two weeks after the clock shift. However, there was also a reduction in workweek morning DVC after clock-shift, but an even greater increase in DVC in the evening. DVC rates are highest around dusk and during the fall, and the fall DST clock-shift caused more workweek commuter traffic to coincide with the annual hourly period of peak risk of DVC. We conclude that in New York State, DST clock-shift results in an increase in the number of DVC, and therefore injuries and property damage associated with such accidents. The justification for DST clock-shifts is controversial; when evaluating the benefits and costs, one should include the consequences for risk of wildlife-vehicle collisions, especially in regions where ungulate-vehicle accidents are frequent, and clock-shifts coincide with the rut or other periods of peak accident risk. • Day Light Saving Time (DST) clock shifts may result in increased road traffic accident risk. • We analyzed 35,167 New York white-tailed deer (Odocoileus virginianus) - vehicle collision (DVC) records that span DST. • DVC increased after the fall DST clock shift, and decreased slightly after spring DST. • Changes in DVC after DST clock shift was greatest on work-week days. • Increased DVC after fall clock shift was due to shifting evening commuter traffic into dusk hours when risk is highest. [ABSTRACT FROM AUTHOR]

The Earth is experiencing excessive nitrogen (N) input to its various ecosystems due to human activities. How to effectively and efficiently remove N from ecosystems has been, is and will be at the center of attention in N research. Hyporheic and riparian zones are widely acknowledged for their buffering capacity to reduce contaminants (especially N) transport downstream. However, these zones are usually misunderstood that they can remove N at all spots and at any moments. Here pathways of N removal from hyporheic and riparian zones are reviewed and summarized with an emphasize on their hot spots and hot moments. N is biogeochemically removed by denitrification, anammox, nitrifier denitrification, denitrifying anaerobic methane oxidation, Feammox and Sulfammox. Hot moments of N removal are mainly triggered by precipitation, fire and snowmelt. Finally, some research needs are outlined and discussed, such as developing approaches for multiscale sampling and monitoring, quantifying the effects of hot spots and hot moments at hyporheic and riparian zones and evaluating the impacts of human activities on hot spots and hot moments, to inspire more research on hot spots and hot moments of N removal. By this review, we hope to bring awareness of the heterogeneity of hyporheic and riparian zones to catchment managers and policy makers when tackling N pollution problems. Unlabelled Image • Riparian and hyporheic zones are misunderstood that they can remove nitrogen at all spots and at any moments. • There are hot spots and hot moments of nitrogen removal from riparian and hyporheic zones. • Hot spots of six nitrogen removal pathways are summarized. • Precipitation, fire and snowmelt can trigger hot moments. • Suggestions for further applications of hot spots and hot moments to nitrogen removal are provided. [ABSTRACT FROM AUTHOR]

The development of low dissolved oxygen (DO) concentrations in the hypolimnion of drinking water reservoirs during thermal stratification can lead to the reduction of oxidized, insoluble iron (Fe) and manganese (Mn) in sediments to soluble forms, which are then released into the water column. As metals degrade drinking water quality, robust measurements of metal fluxes under changing oxygen conditions are critical for optimizing water treatment. In this study, we conducted benthic flux chamber experiments in summer 2018 to directly quantify Fe and Mn fluxes at the sediment-water interface under different DO and redox conditions of a eutrophic drinking water reservoir with an oxygenation system (Falling Creek Reservoir, Vinton, VA, USA). Throughout the experiments, we monitored DO, oxidation-reduction potential (ORP), water temperature, and pH in the chambers and compared the metal fluxes in the chambers with time-series of fluxes calculated using a hypolimnetic mass balance method. Our results showed that metal fluxes were highly variable during the monitoring period and were sensitive to redox conditions in the water column at the sediment-water interface. The time-series changes in fluxes and relationship to redox conditions are suggestive of "hot moments", short time periods of intense biogeochemical cycling. Although the metal concentrations and fluxes are specific to this site, the approaches for examining relationships between metals, oxygen concentrations and overall redox conditions can be applied by water utilities to improve water quality management of Fe and Mn. Image 1 • We measured metal fluxes across sediment-water interface of a eutrophic reservoir. • Fluxes (Fe, Mn) were measured under different redox conditions using two methods. • Time series of fluxes were highly variable, reflecting hot moments of metal cycling. • Fluxes were sensitive to hypolimnetic oxygen and redox potential (ORP). • Under anoxic conditions, ORP is a useful indicator of metal fluxes. [ABSTRACT FROM AUTHOR]